The present invention relates to bottom antireflective coating compositions, polymers useful in making such compositions, and their use in image processing by forming a thin layer between a reflective substrate and a photoresist coating. Such compositions are especially useful in the fabrication of semiconductor devices by photolithographic techniques and provide improved etch-rate for such bottom antireflective coatings.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist.
The trend towards the miniaturization of semiconductor devices has lead to the use of sophisticated multilevel systems to overcome difficulties associated with such miniaturization. The use of highly absorbing anti-reflective coatings in photolithography is a simpler approach to diminish the problems that result from back reflection of light from highly reflective substrates. Two deleterious effects of back reflectivity are thin film interference and reflective notching. Thin film interference results in changes in critical linewidth dimensions caused by variations in the total light intensity in the resist film as the thickness of the resist changes. Variations of linewidth are proportional to the swing ratio (S) and therefore must be minimized for better linewidth control. Swing ratio is defined asS=4(RaRb)1/2e−αD     where Ra is the reflectivity at the resist/air or resist/top coat interface,    where Rb is the reflectivity at the resist/substrate interface,    where α is the resist optical absorption coefficient, and    D is the film thickness.
Bottom anti-reflective coatings function by absorbing the radiation used for exposing the photoresist, thus reducing Rb and thereby reducing the swing ratio. Reflective notching becomes severe as the photoresist is patterned over substrates containing topographical features, which scatter light through the photoresist film, leading to linewidth variations, and in the extreme case, forming regions with complete resist loss. Similarly, dyed top anti-reflective coatings reduce the swing ratio by reducing Ra, where the coating has the optimal values for refractive index and absorption characteristics, such as absorbing wavelength and intensity.